1. Field of the Invention
Embodiments of the present invention generally relate to a method of forming a planar sacrificial layer in a cavity of a MEMS device.
2. Description of the Related Art
MEMS devices typically include a movable plate (i.e., switching element) that is movable between multiple positions, such as between a position in close contact with an electrode and a position spaced from the electrode. Some MEMS devices are used in digital variable capacitors (DVC).
Some DVC devices are based on a moveable MEMS element with a control-electrode above (i.e., a pull-up or pull-off or PU-electrode) and below (i.e., a pull-in or pull-down or PD-electrode) the moveable MEMS element, as shown schematically in FIG. 1. In addition there is an RF-electrode below the moveable MEMS element (i.e., plate or cantilever or movable plate electrode). During operation a voltage is applied to either the PU or PD-electrode, which causes the MEMS element to be pulled-up or pulled-down in contact to provide a stable minimum or maximum capacitance to the RF-electrode. In this way the capacitance from the moveable element to the RF-electrode (which resides below the moveable element) can be varied from a high capacitance Cmax when pulled to the bottom (See FIG. 2) to a low capacitance Cmin (See FIG. 3) when pulled to the top.
Thus, the distance between the movable plate and the RF electrode affects the capacitance. If the movable plate has a non-uniform shape, the capacitance of each MEMS device may be unique and thus, device to device repeatability may be difficult. In order to have repeatable, consistent capacitances, the movable plate should be substantially planar.
Therefore, there is a need in the art for forming a planar movable plate in a MEMS device.